Bicycle seats have changed very little during the last 50 years. Most bicycles have a seat post that telescopes up and down inside an angled portion of the bicycle frame known as the seat tube. At the top of the seat post is a clamping device which allows saddles of various designs to be positioned essentially horizontally with the rearward portion of the seat forming an obtuse angle with the seat post.
My estimate is that roughly 90 percent of the bicycles in the United States are of the railed saddle type. They have the general features shown in FIGS. 1A, 1B and 1C. These features are a cushion 2, a seat post 4 which is typically enlarged near its top, a seat mount boss 6, two saddle rails 8 formed of a single metal bar typically made of spring steel bent into the shape shown in the three figures with both ends of the bar at the front of the saddle. Seat mount boss 6 is used to attach the saddle to the seat post by clamping the two rails. Many saddles are attached to seat post 4 by vertical bolt 10 as shown in FIG. 1A through seat mount 6. In other saddle systems the bolt passes through the boss horizontally. In the vicinity of the seat post and seat mount boss 6, the rails are typically about 11/2 inches apart and parallel to each other so that the seat can be adjusted forward and backward by loosening bolt 10, moving the saddle and then tightening bolt 10. As shown in FIG. 1C the two rails spread apart toward the cantle (i.e., rear) of the saddle so that where the rails meet the cushion 2 they are separated by about 21/4 inches. The vertical distance between the parallel area and the widest separation near the cushion is about 11/2 inches. At the point where the rails begin to separate a knee in defined as indicated at 12 in FIG. 1A. The distance between knee 12 and the corner 14 formed at the rear of the uppermost portion of the straight portion of seat post 4 is variable between about 1 inch to about 3 inches depending of how the saddle is adjusted in the forward-backward direction, but that distance is typically about 21/2 inches.
It is common practice for bicyclists to attach a saddle bag to the back portion of such a saddle and seat post. Two examples are the Goldman patent, U.S. Pat. No. 4,643,343 and the Chan patent U.S. Pat. No. 5,127,563. In Goldman a bracket with a slot is bolted to the rails and one end of a support arm slides through the slot to rest under the seat cover and a bag is supported in a cantilevered fashion by by belting it about the seat post. In Chan a cleat is used to hang an article from the saddle rails and a clip is snapped on the seat post to hold the article in place.
In Smith, U.S. Pat. No. 4,948,020, a carrier frame is held over the back wheel by a cantilever bar bolted to the seat post.